The invention relates to a method of laying a cable or pipe in a fresh-water conduit and a device for performing the said method. The invention is based on a priority application DE 101 05 735.0 which is hereby incorporated by reference.
In the course of the setting-up of new cable installations for telecommunication purposes by regional and local enterprises, alternative solutions to the conventional laying of telecommunications cables directly in the ground are increasingly being considered for economic and/or organisational reasons. An alternative laying technique for telecommunications cables which enters into consideration, in particular for economic reasons, is the use of gas and water conduits which are present in the pipe or duct network belonging to a supply system in a town or village.
A solution of this kind is described in DE 30 01 226 A1. Apart from the reduction in the costs for the setting-up of an urban or regional telecommunications network, as a result of using the existing conduits, excavating operations are only required on a minor scale, so that there is little impairment of the traffic space, which is often limited, particularly in towns. In addition, in the case of this new laying technique, the occupation, which may already be dense in many cases, of routes by conduits belonging to all the supply and waste-disposal departments does not represent any substantial problem, but may even be of advantage.
For the setting-up of a telecommunications network using optical cables having a comparatively small external diameter, including the possibility of connection for subscribers who are to be connected up later, the laying of optical communications cables in fresh-water conduits belonging to the existing supply network therefore enters into consideration for technical and organisational reasons as well as for reasons connected with right of way. In that connection, the greatest importance is to be attached to the neutrality of the cable material, in particular the cable sheath, in respect of drinking water, and also to longitudinal watertightness and permanently secure closure of the cable to permeation by water vapour. Furthermore, when introducing the cable into the conduit, particular care must be taken to ensure that no germ-development or other microbiological contaminations occur in the conduit.
An additional difficulty in the laying of cables in drinking-water conduits consists in the fact that slide valves or other shut-off devices for shutting off the fresh-water conduit are disposed in the said drinking-water conduits at intervals of about 150 to 250 m. At these shut-off points, the cable has to be guided round the slide valve without any adverse effects of a mechanical or optical kind, by guiding the said cable out of the tubular conduit before the slide valve, and guiding it into the said conduit again after the slide valve. In addition, an optical cable also has to be guided out of, or into the tubular conduit for the setting-up of subscriber connections or branches.
DE 297 22 107 U1 describes a device for guiding a cable, in particular an optical communications cable, into and/or out of a fresh-water conduit. This device has a flange-like housing fastened to the fresh-water conduit, at least one guide pipe, which is disposed in the housing and projects into the conduit, for guiding the cable through a continuous bore passing through the wall of the conduit, and at least one sealing element which is disposed in the housing and tightly encloses the cable guided through.
In this device, it can happen under certain circumstances that, particularly after installation, air accumulates, in the form of air cushions which cannot escape, in that upper end of the guide pipe which projects into the housing. This permanently stagnant air promotes the multiplication of bacteria in the guide pipe. These stagnant air cushions should be avoided, without fail, in fresh-water or drinking-water conduits.
In DE-U-29 821 504, this problem is solved through the fact that the guide pipe has, at its end that projects into the housing, at least one aperture that passes through its wall.
Because of the bore that passes through the wall of the guide pipe, air is able to escape from that upper end of the said guide pipe that projects into the housing, and the fresh water transported in the conduit is able to fill up the entire guide pipe. In this way, the accumulation of permanently stagnant air and the formation of an air cushion in the guide pipe, which promote the multiplication of bacteria, are reliably avoided.
In the known proposals, it is not possible to avoid germs, bacteria and other contaminants entering fresh-water conduits.
The underlying object of the present invention is therefore to improve the method initially mentioned in such a way that the introduction of germs, bacteria and contaminants is avoided to a very great extent.
This object is achieved by a Method of laying a cable, or a pipe for the subsequent introduction of a cable, in particular an optical communications cable, in a fresh-water conduit. Said method comprises the step of cleaning the surface of the cable or pipe is cleaned during the laying process immediately before entering the fresh-water conduit.
According to a particularly advantageous refinement of the invention, provision is made for cleaning to be performed with a liquid, preferably water, which is directed onto the surface of the cable or pipe under high pressure. The surface of the cable or pipe may alternatively, or even additionally, be cleaned with rotating brushes. These mechanical modes of operation make it possible to remove dirt and dust. In order to remove greases or other organic substances located on the surface of the cable or pipe, it is appropriate, or rather necessary, to add suitable solvents to the liquid, but these should be water-soluble and not contaminate the drinking water. After this coarse mechanical treatment, the surface of the cable or pipe is intensively rinsed in order to rinse off residues of dust and dirt and also solvents.